unpin nixpkgs here, see if it helps the overall deployment

come back and explain this if it does :/

nixpkgs.nix

 { pkgs ? import <nixpkgs> { } }:
 let
-  nixpkgs = fetchTarball
-  { url = "https://github.com/NixOS/nixpkgs-channels/archive/4557b9f1f50aa813ae673fe6fcd30ca872968947.tar.gz";
-    sha256 = "0cam48cn042axcik9vqxsqjc2hwyb2grjbjxacsn4w0y1zk6k6l2";
-  };
+  nixpkgs = pkgs.path;
   args =
   { overlays = [ (import ./overlays.nix) ];
   };